The agricultural waste materials suitable as starting materials for the manufacture of the absorbent materials of the present invention are being produced in large quantities. The waste material from citrus juice processors consisting of peels (i.e. albedo and flavedo) and rag, is generally processed to cattle feed by what has been termed the "lime de-watering process". This process comprises the steps of treating the waste with "lime" (calcium oxide, calcium hydroxide, or even calcium carbonate) to convert it from a slimy, unpressable condition to a watery, pressable condition; pressing the converted waste; and drying (see, for example, U.S. Pat. No. 2,147,521, issued Feb. 14, 1939 to Florida Citrus Exchange; U.S. Pat. No. 2,215,944, issued Sept. 24, 1943 to Vincente; U.S. Pat. No. 2,362,014, issued Nov. 7, 1944 to Citrus Processes, Inc.).
Relatively small quantities of citrus waste are used as a source of pectin, which can be used as thickening agent in food products. Food thickening agents may also be prepared by comminuting citrus peel material, and lowering the degree of esterification of the pectic materials in the citrus peel by enzymatic or chemical treatment. This approach has been disclosed in U.S. Pat. No. 3,982,003 issued Sept. 21, 1976 to Mitchell et al., and in U.S. Pat. No. 4,143,172, issued Mar. 6, 1979 to Mitchell et al. Another attempt at converting citrus waste to a food additive for human consumption is disclosed in U.S. Pat. No. 4,225,628, issued Sept. 30, 1980 Lynn. According to the process described in this reference, citrus peel particles are de-watered by a process very similar to the lime de-watering process used in cattle feed production; the material is subsequently mixed with sesame grain flour, ground, dried and milled to a desired particle size. U.S. Pat. No. 4,379,782, issued Apr. 12, 1983 to Staub et al. discloses the use of citrus albedo or sugar beet pulp as a dietary fiber. The material is extracted with water or isopropanol to remove soluble carbohydrates and color and flavor materials. In spite of these attempts at finding more profitable uses for citrus waste, almost all of the citrus waste from juice canneries is still being converted to cattle feed and sold at a price which barely provides for recovery of the processing costs.
Sugar beet residue (commonly referred to as beet pulp), like citrus residue, is generally converted to cattle feed. As for citrus residues, attempts have been reported to convert beet pulp into a food additive suitable for human consumption. An example is Japanese Pat. No. SHO 57-54573, publication date Apr. 1, 1982. This patent discloses a method for upgrading beet pulp by bleaching the pulp in hypochloric acid at pH 6.5 to 7.5, washing with water and drying. The material is reported to be capable of absorbing about 90% of its weight in water.